Add per-backend input debug visualization + round-trip view

Makes it possible to isolate an input->tool problem from a tool->game one in the
Controllers panel (under Debug details):
- which backend fed each slot is already shown via the per-pad source tag
  ("XInput #0" / "Steam Input") in the Incoming section;
- a new "Round-trip" table shows, per slot, the state we forwarded (the active
  backend's pad) next to what the game actually read back, highlighting matches.

For the round-trip, the XInput hook now echoes the state it returns to the game into
the status (protocol v9->v10: per-slot read_state in HookStatus).

Verified: hook_selftest (x64 + x86) asserts the hook records the game-read state;
full build x64 + x86 clean; ctest x64 9/9, x86 3/3.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

README.md

@@ -76,15 +76,6 @@ is removed from this list once done — so the top item is always next. The
 self-verifiable tooling / UI / input items come first; the game-pipeline items that
 need a real game (and Remote Play) to fully validate come last.
 
-- **Per-backend input debug visualization.** To separate "wrong input *into* the
-  tool" from "wrong input *out to* the game", show three distinct views in the
-  Controllers panel (under Debug details): (a) **received via XInput** (raw
-  `XInputSource` state), (b) **received via Steam Input** (raw `SteamInputSource`
-  action values) — so it's obvious which backend delivered what — and (c)
-  **forwarded to the game** (the `PadInfo` we write to shared memory, alongside what
-  the game actually read back via the hook's per-slot channel). The hook already
-  reports per-slot poll counts; extend it to echo the last state the game read so (c)
-  is a true round-trip.
 - **Release the mouse cursor for cursor-clipping games.** Games that confine the
   cursor while focused (e.g. Trails through Daybreak via `ClipCursor` / per-frame
   `SetCursorPos` re-centering) trap the operator's mouse permanently, because the

common/include/coop/protocol.hpp

@@ -12,7 +12,7 @@ namespace coop
 
 // Bump whenever the layout of SharedBlock or CoopPadState changes. The hook
 // refuses to attach to a host with a mismatched version.
-inline constexpr std::uint32_t kProtocolVersion = 9;
+inline constexpr std::uint32_t kProtocolVersion = 10;
 
 // 'COOP' little-endian, used to sanity-check the mapping before trusting it.
 inline constexpr std::uint32_t kProtocolMagic = 0x504F4F43u;
@@ -133,6 +133,10 @@ struct HookStatus
 	// other diagnostics -- benign cross-process races are fine.
 	std::uint16_t rumble_left[kMaxPads];
 	std::uint16_t rumble_right[kMaxPads];
+
+	// The last pad state the hook actually returned to the game per slot, so the host
+	// can show a true input round-trip (forwarded vs what the game read).
+	CoopPadState read_state[kMaxPads];
 };
 
 // Host -> hook control channel. The host requests which hook subsystems should be

hook/src/ipc_client.hpp

@@ -151,6 +151,15 @@ public:
 		}
 	}
 
+	// Record the state the hook just returned to the game for a slot (round-trip view).
+	void note_read_state(std::uint32_t slot, const CoopPadState& state)
+	{
+		if (block_ != nullptr && slot < kMaxPads)
+		{
+			block_->status.read_state[slot] = state;
+		}
+	}
+
 	// --- Audio render-hook diagnostics -------------------------------------
 
 	// Total distinct render streams the audio hook has observed.

hook/src/xinput_hook.cpp

@@ -90,6 +90,10 @@ DWORD query_state(DWORD user_index, XINPUT_STATE* state, bool keep_guide)
 		result.Gamepad.wButtons &= ~kGuideButton;
 	}
 	*state = result;
+	if (g_ipc != nullptr)
+	{
+		g_ipc->note_read_state(user_index, pad); // round-trip: what the game just read
+	}
 	return ERROR_SUCCESS;
 }
 

host/src/controllers_panel.cpp

@@ -182,6 +182,37 @@ void ControllersPanel::draw(const InputSource& input, const HookStatusView& stat
 		ImGui::EndTable();
 	}
 
+	// Round-trip view: what we forwarded (the active backend's pad, tagged per slot in
+	// the Incoming section above) vs what the game actually read back through the hook.
+	// A mismatch isolates a tool->game forwarding problem from an input->tool one.
+	if (debug_details)
+	{
+		ImGui::SeparatorText("Round-trip (forwarded vs game read)");
+		if (ImGui::BeginTable("roundtrip", 3, ImGuiTableFlags_Borders | ImGuiTableFlags_SizingStretchProp))
+		{
+			ImGui::TableSetupColumn("Slot");
+			ImGui::TableSetupColumn("Forwarded  btn / LX,LY");
+			ImGui::TableSetupColumn("Game read  btn / LX,LY");
+			ImGui::TableHeadersRow();
+			const auto& fwd = input.pads();
+			for (int i = 0; i < static_cast<int>(kMaxPads); ++i)
+			{
+				const CoopPadState& f = fwd[i].state;
+				const CoopPadState& r = status.read_state[i];
+				ImGui::TableNextRow();
+				ImGui::TableNextColumn();
+				ImGui::Text("%d", i);
+				ImGui::TableNextColumn();
+				ImGui::Text("0x%04X  %d,%d", f.buttons, f.thumb_lx, f.thumb_ly);
+				ImGui::TableNextColumn();
+				const bool match = f.buttons == r.buttons && f.thumb_lx == r.thumb_lx && f.thumb_ly == r.thumb_ly;
+				ImGui::TextColored(match ? kGreen : kGrey, "0x%04X  %d,%d", r.buttons, r.thumb_lx, r.thumb_ly);
+			}
+			ImGui::EndTable();
+		}
+		ImGui::TextDisabled("Slot tags in 'Incoming' above show which backend (XInput / Steam) fed each slot.");
+	}
+
 	ImGui::End();
 }
 

host/src/ipc/ipc_server.cpp

@@ -89,6 +89,7 @@ HookStatusView IpcServer::hook_status() const
 	{
 		view.rumble_left[i] = s.rumble_left[i];
 		view.rumble_right[i] = s.rumble_right[i];
+		view.read_state[i] = s.read_state[i];
 	}
 	return view;
 }

host/src/ipc/ipc_server.hpp

@@ -40,6 +40,9 @@ struct HookStatusView
 	// Per-slot rumble the game requested (host forwards it to the guest's pad).
 	std::uint16_t rumble_left[kMaxPads] = {};
 	std::uint16_t rumble_right[kMaxPads] = {};
+
+	// The last pad state the hook returned to the game per slot (round-trip view).
+	CoopPadState read_state[kMaxPads] = {};
 };
 
 // Plain snapshot of the Present-hook video channel for the Video mirror panel.

tests/hook_selftest.cpp

@@ -175,6 +175,10 @@ int main()
 	check(block->status.rumble_left[0] == 0x8000 && block->status.rumble_right[0] == 0x4000,
 	      "status records rumble from XInputSetState");
 
+	// Round-trip: the hook echoes the state it returned to the game (for the
+	// Controllers panel's forwarded-vs-read view).
+	check(block->status.read_state[0].buttons == (kButtonA | kButtonB), "status records game-read state");
+
 	hook::remove_xinput_hooks();
 
 	std::printf(g_failures == 0 ? "SELFTEST PASS\n" : "SELFTEST FAILED (%d)\n", g_failures);